Photographic films on heat resistant cellulose triacetate

ABSTRACT

For some uses in the photographic field, practically perfect dimensional stability (resistance to visible distortion and shrinkage less than 0.5 percent is required of sensitized film which is exposed to temperatures as high as 240*-250* C for a few seconds without edgewise restraint. Conventional cellulose ester films cannot meet such rigid requirements. It has now been found that cellulose triacetate film that (a) contains at most a few percent of plasticizer, (b) is fairly highly crystalline, and (c) is substantially free of visible distortion and haze (less than about 3 percent can meet these requirements that involve excellent high temperature dimensional stability).

United States Patent Dotson et al. 1 Dec. 5, 1972 [5 PHOTOGRAPHIC FILMS ON HEAT 3,128,148 4/1964 Moore et al. ..8/131 RESISTANT CELLULOSE TR] ACETATE OTHER PUBLICATIONS U [72] Inventors; Billy Dotson; Robert Dimensional Stability of Kodak Acetate Films for the Schrader; Marflyn Twomey; Graphic Arts, Eastman Kodak Company, Rochester 4, R b Williams, Jr" n of R N.Y., Kodak Pamphlet NO. Q- 33, 6- 60 Minor Reviester sion, 219- L- lPS- C, 3 pages.

[73] Assignee: Eastman Kodak Company, Roch- Primary Examiner-D0nald E. Czaja Assistant Examiner-Ronald W. Griffin [22] Filed: April 3 1970 Att0rneyWalter O. Hodsdon and John T. Lewis 1 1 pp 25,571 57 ABSTRACT k Related US. Application Data For some uses in the photographic field, practically a perfect dimensional stability (resistance to visible [63] fgg fg zlgzg distortion and shrinkage less than 0.5 percent is g required of sensitized film which is exposed to tem- [52] Uls. CL 260/227 96/87 106/177 peratures as high as 240-250 C for a few seconds 161/411 60/230 without edgewise restraint. Conventional cellulose [51] im. Cl. ..cosb 21/04 ester films meet Such rigid requirementshas Field f Search 2 0 227 230 R; 9 7. 110W been found that cellulose triacetate film that (a) 106/177; 161/265 contains at most a few percent of plasticizer, (b) is fairly highly crystalline, and (c) is substantially free of l 5 References Cited visible distortion and haze (less than about 3 percent can meet these requirements that involve excellent UNITED STATES PATENTS high temperature dimensional stability).

2,703,290 3/1955 Scott et al ..96/87 3 Claims, N0 Drawings 2,812,279 11/1957 Nadeau ..161/269 3,291,625 12/1966 Faraone et a1 ..106/177 3,447,927 6/1969 Bacon et a1 ..96/87 PHOTOGRAPHIC FILMS N HEAT RESISTANT CELLULOSE TRIACETATE This is a continuation-in-part application of US. application Ser. No. 439 filed Jan. 2, 1970, now abandoned, by Billy Dotson, Robert Schrader, Marilyn Twomey and Robert F. Williams, J r.

This invention relates to special photographic film elements made using special cellulose acetate film base that-is resistant to distortion caused by exposure to temperatures as high as about 240 C.

\ manent image forms on the surface of the film element,

which must, of necessity, remain visibly undistorted by the ,hot treatment. Examples of useful, print-out emulsions and film elements can be found in US. Pat.

No. 3,447,927, issued June 3', 1969.

In order to evaluate film base materials for use in such hot development systems, two tests have been developed. The first test, which involves a 6second physical contact with a polytetrafluoroethylene-coated steel plate having a temperature of 240 C, is designed to simulate the somewhat extreme conditions to which the final film elements described above can be subjected during development of the image thereon. Acceptable films, by this test must remain substantially free of visible distortion and shrink less than 0.3

- percent. In the second test, films are lowered through a well into an oven at 240 C, and held unrestrained for 60 seconds. This second test is more severe than the first, producing somewhat more shrinkage. It can readi- Iy be appreciated that very few types of film base materials have been found that meet these stringent requirements. Examples of the few film types that can meet such rigid requirements are poly(l,4-cyclohexylenedimethylene terephthalate) and polycarbonates. Although cellulose acetate is a relatively inexpensive film base material, conventional cellulose acetate film base distorts and shrinks excessively when it is subjected to the hot" tests described above. For example, mil conventional cellulose acetate photographic film wrinkles severely and shrinks more than 12 percent when it is subjected to these tests.

It has now been discovered that, if relatively amorphous, relatively plasticizer-free cellulose triacetate film is heat-treated to become at least about percent crystalline in form (wherein this crystallinity is distributed fairly uniformly through the film) in such a manner that the resulting film is substantially free of visible distortion, such film, surprisingly, is found to have the desired high temperature dimensional stability described above. At the present time, only two methods are known for manufacturing this type of valuable cellulose triacetate film. These methods constitute the subject matter of two patent applications. One method involves the quick (at most about 65 seconds) exposure of film to a temperature of from about 230 C to about 270 C, followed by a quick reduction in temperature of the hot, treated film. Very low lengthwise tension is used in this process, which is the subject of US. Pat. application Ser. No. 441, filed Jan. 2, 1970, now abandoned, entitled Improved Process for Heat Stabilizing Cellulose Triacetate Films or Sheets by Robert W. Schrader. The second method involves slowly raising the temperature of the relatively substantially amorphous cellulose triacetate film through the temperature region of from about 180 C to about 220 C, while the film is maintained under, at most, very little restraint. This method is the subject matter of US. Pat. application Ser. No. 440, filed 'Jan. 2, 1970, now US. Pat. No. 3,608,059, issued Sept. 21, 1971, entitled Improved Process for Heat Stabilizing Cellulose Triacetate Films or Sheets by Billy R. Dotson, Marilyn A. Twomey, and Robert F. Williams, Jr. Such specially heat-stabilized cellulose triacetate films are the subject to which this application is directed. The percent crystallinity of the special, heat-stabilized cellulose triacetate films of the present invention can be determined in accordance with the method of PH. Hermans and A. Weidinger, as published in Die Makromolekulare Chemie, Vol. 44, page 24 1961).

Using the method of Hermans and Weidinger. to

determine the fraction of crystallinity in the film product of Example 1, below, it is found that the crystalline fraction (or percent crystallinity) in this film is 13.4 percent, whereas the percent crystallinity of the film, before being heat-stabilized, had been essentially zero. The method is based on the conclusion that the crystallinity. of a sample is equal to the area under its diffractogram due to crystallinity divided by the diffractogram area for a 100 percent crystalline sample (or conversely when the basis of comparison is essentially amorphous).

Apparently, for acceptable results, the films of the present invention must have a thickness of from about 0.5 to about 30 mils (preferably from about 3 to about 10 mils), and be at least about lO-percent crystalline, with the crystalline nature of the films apparently being fairly uniformly distributed through the thickness of the films (as compared to surface-crystallized" films obtained by treatment with an organic liquid such as methylene chloride or phenol). Similarly, the requirement that the films of this invention be free of visible distortion (wrinkling and the like) cannot be overemphasized, since only films having this characteristic are commercially acceptable. Whereas, crystallized, heat-treated cellulose triacetate films have been made heretofore, they have not had this distortionfree" characteristic, combined with the necessary very low shrinkage values that are exhibited by the films of this invention. Apparently too much crystallinity in cellulose triacetate films results in too much opacity or haze in the films. Films of the present invention have at most about 3 percent of haze.

Note that the films of this invention are made of cellulose acetate material that can contain at most about 1 weight percent of hydroxyl and at least about 41 weight percent acetyl, and which has an intrinsic viscosity, measured in a :10, by volume, mixture of methylene chloride and methanol, of at least about 1.0.

EXAMPLES l-6 Films of unplasticized cellulose triacetate (containing 43.3 percent acetyl, 1 percent hydroxyl and having an intrinsic viscosity of about 2.2, measured by ASTM test No. D871-63, Sections 42-45, using a 90:10 methylene chloridezmethanol mixture) that have been conventionally solvent cast and air dried, and which are substantially amorphous and approximately 5 mils thick are heat treated in a conventional forced-draft oven by passing the films continuously into and out of the oven. The time in the oven is recorded. Also, various oven temperatures, heat-treating time periods and tensions are utilized. The films are then suddenly quenched, when they are removed from the oven, by quickly exposing them to a stream of ambient air. Then the heat-treated films are subjected to the 60- secondl240 C hot oven" test described above. Percent shrinkage is also recorded. Results of tests such as these are set out in Table I.

Films of unplasticized cellulose triacetate (containing 43.3 percent acetyl, 1 percent hydroxyl and having an intrinsic viscosity of about 2.2) that have been solvent cast and air dried conventionally, and which are substantially amorphous (non-crystalline) and approximately 7 mils thick are suspended without restraint in a conventional forced draft oven having an initial temperature of 180 C. The temperature of the oven is then gradually and evenly raised at a uniform rate over a minute period to220 C. At this point the films are removed from the oven and cooled quickly to ambient temperatures. These films are found to have shrunk about 6 percent during the heating step. However, the films are surprisingly, essentially free of distortion, even though they have been treated without edgewise restraint. This film is an excellent base when it is coated with a typical sub" and a print-out emulsion, exposed, and developed, as described in U.S. Pat. No. 3,477,927.

For a comparison test, several identical films are simply annealed at 220 C for 15 minutes. No edgewise restraint is applied to these films, either. These films are found to have shrunk about 12 percent and are severely distorted and wrinkled by the end of this heattreating step. ln Table ll is tabulated the shrinkage data resulting from contacting the film for 6 seconds against a steel platen having a temperature of 240 C.

TABLE II Sample %Shrinkage 0.1% (no distortion) 1.0% (high distortion) The plasticizers mentioned above that can be present, if desired, in the cellulose triacetate films of the present invention are all of those that can ordinarily be used in cellulose acetate photographic film base and wrapping sheeting materials. This includessuch well known materials as triphenylphosphate and the like. Other materials can also be present in the film products of this invention in minor amounts, so long as the basic fairly highly crystalline nature of the film products is not excessively impaired thereby. This includes dyes, pigments, chemical stabilizers and the like. At most about 5 weight percent of such plasticizer material(s) should be present in the films of this invention, while preferably substantially none should be present in such films for optimum results. Otherwise the films exhibit too high shrinkage values when they are exposed to the very high temperatures described above.

This invention has been described in detail with particular reference for and to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of this invention.

We claim:

1. Cellulose triacetate film base having improved resistance to distortion and shrinkage when exposed to very high temperatures without edgewise support, said film base being characterized by a. consisting essentially of cellulose acetate material having at most about 1 weight percent of hydroxyl and at least about 41 percent acetyl and having an intrinsic viscosity, measured in a :10, by volume, mixture of methylene chloride and methanol, of at least about 1:

b. being substantially free of visible distortion;

c. being at least about 10 percent crystalline, the crystallinity being uniformly dispersed through the thickness of said film;

d. having at most about 3 percent haze, measured through the thickness of said film;

e. containing at most about 5 weight percent of plasticizer;

f. being from about 0.5 to about 30 mils thick; and

g. having a shrinkage, without distortion, of at most about 0.5 percent when held in contact with the surface of a 240 C steel platen for 6 seconds.

2. Heat stabilized cellulose triacetate film base as in claim 1, wherein the thickness of said film base is from about 3 to about 10 mils, and said film base is essen: tially free of plasticizer.

3. Heat stabilized cellulose triacetate film base as in claim 2, wherein said film base is cellulose triacetate material containing about 43 percent acetyl, about 1 percent hydroxyl, and has an intrinsic viscosity of about 

2. Heat stabilized cellulose triacetate film base as in claim 1, wherein the thickness of said film base is from about 3 to about 10 mils, and said film base is essentially free of plasticizer.
 3. Heat stabilized cellulose triacetate film base as in claim 2, wherein said film base is cellulose triacetate material containing about 43 percent acetyl, about 1 percent hydroxyl, and has an intrinsic viscosity of about
 2. 